Until you actually figure out the problem? Turn off your screen saver. You don't actually *need* one - the pixel burn-in thing has long been solved, and that's what they were for. If you use it to hide stuff...uh...i guess minimize is your friend, but i'd just turn it off until you work out the underlying problem.

Are you using an LCD or a CRT monitor? I had a CRT crap out on me last year, and the image flickering is a good sign that the monitor is on the way to doing so. There should be some diagnostics on your system that you can run (for both the video card and the monitor), although the best test is to just plug in another monitor, if you can.

If you can give me any more specifics, I can run it by my techie friends.

Is it running hot? Do you vacuum it regularly? Is the fan working okay? Because heat'll kill your 'puter faster than anything, and the fact that it starts up okay after a few hours--maybe after it's had a chance to cool down?--might be an indicator.